The Eclipse Marketplace Client, Photon edition has a bug where it fails to open in certain cases. If nothing happens when you try to access the Eclipse Marketplace via “Help > Eclipse Marketplace”, please update the Marketplace Client plug-in by doing the following:

Follow the wizard and restart your Eclipse to finish the installation.

We are working on providing an update to the Eclipse Photon release to distribute the fix through automatic updates and package downloads. In the meantime, please update manually if you are affected by this bug.